Steam generating, superheating and reheating unit with reheater ahead of the superheater



Qct. 21, 1958 v p. H. KOCH 2,856,907

STEAM GENERATING, SUPERHEATING AND REHEATING UNIT WITH REHEATER AHEAD OF THE SUPERHEATER Filed Nov. 30. 1955 2 Sheets-Sheet 1 INVENTOR. Paul H. Koch BY Oct. 21, 1958 P. H. KOCH 2,856,907

STEAM GENERATING, SUPERHEATING ANDREI-EATING UNIT WITH REHEATE'R AHEAD OF THE SUPERHEATER Filed Nov. 30. 1955 2 Sheets-Sheet 2 INVENTOR. Paul H. Koch ATTORNEY United States Patent STEAM GENERATING, SUPERHEATING AND RE- HEATING UNIT WITH REHEATER AHEAD OF THE SUPERHEATER Paul H. Koch, Bernardsville, N. J., assignor to The Babcock & Wilcox Company, New York, N. Y., a corporation of New Jersey Application November 30, 1955, Serial No. 550,063

' 1 Claim. 01. 122----478) This invention relates to the combined generation, superheating, and reheating 'of high pressure and high temperature steam adapted for use in efiiciently producing power in a power plant involving a plural stage steam turbine.

The invention is exemplified in an integrated unit involving a high temperature furnace, with the gases from the furnace first passing over the heat absorbing surfaces of a reheater before passing over the heat absorbing elements of a high temperature superheater receiving steam from steam generating tubes connected into a fluid circulation system and disposed as wall tubes along the boundary surfaces of the furnace, and a gas recirculation system withdrawing low temperature gases from a point inthe gas fiow beyond the superheater and introducing those gases into the furnace at a point near the reheater for control of the gas temperatures contacting the reheater.

The invention will be concisely set forth in the claim, but for a complete understanding of the invention, its

uses, and advantages, recourse should be had to the 1 of Fig. 1.

The drawings show a cyclone furnace of a type, the details of which are illustrated and described in the patent to Kerr et al. 2,594,312. This cyclone furnace burns a slag forming fuel, such as particle form coal at temperatures substantially above the fusion temperature of the slag so that the fused slag flows to the bottom of the cyclone furnace and exits into the primary furnace chamber 12 through the slag exit opening 14. The high temperature gases with small particles of fused solids in suspension pass from the cyclone furnace chamber through its throat 16 into the primary furnace chamber 7 '12, and then flow upwardlybetween and over the screen formed by the rows of tubes 18. The high temperature gases with their suspended solids thence flow into the secondary furnace chamber 20, the walls of which such as the front wall 22, the rear wall 24 and the connecting side walls 39, 41 include upright steam generating tubes connected into the fluid circulation system of the unit and normally discharging steam and water mixtures into the steam and water drum 26. These tubes are connected into the fluid circulation by the downcomer 28 and other appropriate circulatory connections with the submerged drum 30, from which extend the steam generating tubes forming or lining the above indicated walls, as well as the floor 32, and the inclined bafile wall 34 separating the primary furnace chamber 12 from the secondary furnace chamber 20. The side Walls of the furnace chamber include similarly connected steam generating wall tubes discharging at their upper ends into side wall headers 40, and leading upwardly from lower headers 42 which are appropriately connected to the downcomer 28 by circulators 44. Similar circulators 46 connect the lower end-of the downcomer with cyclone furnace headers 48 and 50, into which the cyclone furnace wall tubes are connected.

In accordance with the invention, the high temperature slag-laden heating gases flowing upwardly in the secondary furnace or radiation chamber 20 first contact heat absorbing surface of a steam reheater 52. The reheater has a radiantly heated section formed by longitudinally spaced rows 62 and 64 of transversely spaced tube platens defined by a plurality of multi-looped nested tubes, corresponding tubes in the rows 62, 64 being series connected to provide parallel steam flow paths from the reheater inlet header 54 to an intermediate header 56. In addition to the radiant section, the reheater has a convection heated section formed by a row of U- tube platens 58 in the entrance end of the rearwardly tapering convection heating gas. pass extending rearwardly from the .upper end portion of the radiation chamber 20. The ends of the tubes 58 are connected to the intermediate header 56 and the reheater outlet header 60, thus providing a series flow of steam being reheated first through the reheater radiantsection and then through the convection section. With this location and arrangement of the reheater heat absorbing surface, the desired high reheat temperature can be readily maintained over. a relatively wide load range due to the inherently flat reheat temperature curve of serially connected radiant andconvection sections.

For protection of the banks of reheater tubes 62 and 64, and to maintain effective heat transfer from the high temperature gases to these tubes, the gases and their suspended fused slag particles have their temperatures lowered by the gas recirculation system including the fan 70, the fan inlet ductwork 72 communicating with the flow of heating gases at the port 74, beyond the superheater, and fan outlet ductwork 76 leading through a port 78 intoa recycled gas chamber 80, from which the lower temperature recycled gases flow in the direc- 1 tion indicated by the arrows 82 and through the openings 84in the furnace wall 24. These openings are provided by bending portions of some of the wall tubes, such as the tubes 86 (Fig. 1) out of their wall alignment. The openings 84 and the arrangement of adjoining portions ofthe wall tubes is clearly indicated in Fig. 2, as is the direction of flow of the recycled lower temperature gases indicated by the arrows 88.

As 'the demand for steam increases, the rate of firing of the cyclone furnace increases, and the temperature of the'gases approaching the reheater 52 tends to simultaneously and correspondingly increase. Under these circumstances the rate of flow of the lower temperature recycled gases through the gas'recirculation system and into the secondary furnace chamber 20 is increased in order to maintain the temperature of the gases contacting the reheater 52, within allowable limits, and to so change the temperature of the suspended particles of slag within the gases that they are not in a sticky state as they contact the heat absorbing elements of the reheater.

Under conditions of decreasing the load with a correspondingly decreasing rate of firing of the cyclone furnace 10, the rate of flow of the recycled lower temperature gases into the secondary furnace chamber 20 would be decreased, but this decrease may be modified for the purpose of affecting the temperature of the reheated steam by controlling the mass flow of gases over the tubes of the reheater, and the following superheater.

The superheater has an inlet header 90 receiving,

"through the circulators 92, steam separated from the steam-and avatermixtures within the steam-and water drum 26. From the header 90 a plurality of superheater tubes lead downwardly. The first sections of lead downwardly along the gas'pass walls 102 and 104 flows upwardly" through aplurality-of"tubes 108, the {subsequentsections of which form serially connected return bend -tubeswonstituting the banksof tubes 110 -112.

The outlet ends of these tubes 114=are connected tome header 1 16, from which appropriate cir'culatorycbnnections.- 118 -lea'd to tha -secondary:superheaterheader- 120. From. the header 120 there extends a row" of tubes having serially connected return bend-section's forming-the A bank c of .1 secondary: superheater tubes:'.122. From "the outlet --1 section ofthisbank of t ube s these tubes pass horizontally 'betweeni; successiven upri'ght-t superheater' -'tubes' leading from' thezheader't 9flsand between'the" steamgenerating temperature stearnspassesv to.:th"e=:high' pressure and high temperature-section of. ai'steami turbine, or another appropriate point" of use.

Thea-high temperature gases after havingpassed over the banks ofJtubes-62zand 64 of the reheaterpass across the abovedescribed banks of tubesofthe superheater,

- and-thenacrosszthe bank of tubes-130 connected to the inlet and outlet headers-132 and 134. of the economizer into the duct-work above the hopper-134, from which a duct or flue 136:1eads past the recycledgas port 74 v to a flue or stack.

The steam generating, superheating, and reheating unit of the invention is preferably provided with such a control system that, as the demand for steam and. the fuel firing rate increase, the flow of recycled gases into the furnace chamber increases. Reversely, as the load decreases'and as the firing rate decreases, there will-be 4 Troutman 542,925, and Stallkamp 542,926, filed October 26, 1955 for so controlling the operation of the recycled gas system and more particularly the gas flow in the vicinity of the recycled gas fan that reverse flow of gases from the furnace chamber toward the recycled gas fan is prevented.

Although the invention has been described with reference to the details of a preferred embodiment, it is to be recognized that the invention is not limited to all the details thereof. It is rather'to be considered-as of a scope commensurate with the scope of the-sub-joined claim.

' What is claimed is:

A vapor generating, superheating and reheating unit comprising walls defining avertically elongated radiation chamber having a laterally extending convection heating gas pass opening to the upper end thereof and a downflow gas pass connected to the opposite end of said convectiongas pass, vapor generating tubes lining the .walls of :said-radiation chamber, a cyclone furnace for burning a. slag-forming -.particulate fuel in suspension at temperatures above the fuel: ash fusion temperature and causing slag-carrying high temperature-heating gases tosenter the lower end of said radiation chamber and flowv-upwardly. in saidrradiation chamber, a row of pendent tubesplatens in stheupperspartof said radiation chamber arranged to. receive :heat-"mainly byradiation an'cl forming a'radiant-vapor reheating section, a second rowofpendent tube platens in said'convection heating gas pass arranged to'ireceive heat mainly by convection :and -forming a--convection vapor reheatingsection, a

.- group Ol rSfiCOIldfiI'Y-W'EPOI superheating tubes inxsaid convection.heating-gas pass'rearwardly of said convecnon vaporreheatingsection, a group of primary vapor a decreasein the flow'of recycled'gases. :Thatwpart of cthecontrol "system affecting the flow of recycled'=gases may function from a plurality of,operative-.-variables such as representations of gas temperature at a position inithesecondary furnace chamber'and cl'oseito-the v.reheater; Other variables from Which'the flow of recycled .gasesis controlled -may.includet representations ofrthe .fuel burning. .rate.

" maybe representatives of reheat and superheatsteam temperature or temperatures. Thecontrol system of the illustrative unit may alsoinvolvesuch controls 'of-the recycled gassystem aslare indicated inmthe common assignees co-rpendingnapplications to -Moonan 542,927,

superheating tubes' in said downfiow gas: passserially connected to said secondary vapor superheating: tubes, all of said primary and secondary vapor .sup'erheating tubes being located in the gas'fiow path downstream-of saidconvection vaporreheating section, a gI'OLlp;'()f

economizer tubes in saiddownfiow gas pass below said primaryvapor superheating tubes, means forming a series of transversely spaced gas inletportsin one Ofl'lflle vertical walls of said radiation chamber at a'level between the point ofwentry of theh'eatinggaseswand thex'l'ower end of saidfirst row of reheater-tube platens, and.-means for withdrawing heating gases from a point in s'aiddownflow gas-pass below said-economizer tubes and "introducing the withdrawn gas into said radiation chamber through said gas inletsports.

' LReference'slCited in the-file of this patent l UNITED STATES PATENTS 2,685,279 Caracristi Aug. 3, 1954 2,730,080 Stallkamp Jan. 110, 1956 2,737,930 Rowand et' a1. Mar. 13, 1956 2,781,746 Armacost' et a1. Feb. 19, 1957 FOREIGN PATENTS 675,410 Great Britain Ju1y,.9, 1952 

